The present invention relates generally to anti-G suits, and more specifically to flexible lower body negative pressure (LBNP) trousers for protection from the adverse affects of -G.sub.z acceleration and for other uses.
Conventional anti-G suits, such as are described in U.S. Pat. No. 4,674,479 to Jennings et al for an improved anti-G suit, protect pilots and other aircrew of high performance aircraft from the adverse physiological effects of high acceleration in the positive z direction (upwards relative to an aircraft), commonly written as +G.sub.z. Adverse physiological effects, however, also result from acceleration in the negative z direction, written as -G.sub.z, and at acceleration levels lower than are normally considered harmful in the positive z direction.
In addition to -G.sub.z accelerations that may occur during a variety of flight maneuvers, such as steep dives and outside loops, -G.sub.z accelerations can also occur during atmospheric reentry of transatmospheric space vehicles, particularly smaller, more streamlined space vehicles that may exist in the future.
The limit of a unprotected aircrew member's tolerance against the adverse physiological effects of -G.sub.z acceleration is about -2.5 G.sub.z. His or her tolerance limit against the severely unpleasant subjective sensations from -G.sub.z acceleration is only about -2.0 G.sub.z. The adverse physiological effects can be separated into two primary groups. In the first group, blood shifts to the head and increases cerebral venous and arterial pressures. The resulting increased pressure in the capillary system disrupts the normally balanced Starling forces, which move tissue fluids in and out of the capillaries, and causes edema. Further pressure increases, particularly venus pressures above 70 mmHg, may cause pain, increased facial edema, conjunctival hemorrhages, vision difficulties, sinus pain, headaches, severe nose bleeds and bleeding into the nasal sinuses.
The second group of adverse physiological effects of -G.sub.z acceleration are the most dangerous, particularly severe bradycardia. The increase in cephalad (headward) arterial pressures stimulates the baroreceptors in the carotid sinuses and in the wall of the aortic arch to cause a reflex increase in vagus nerve impulse which decreases heart rate. The baroreceptors are very sensitive to large changes in arterial pressures, especially from baseline values. Negative G.sub.z acceleration has been shown to cause periods of asystole (cessation of the pumping heart contraction), sinus arrest (long pauses between heart beats) and occasional incapacitation.
Prior art attempts to protect against the negative effects of -G.sub.z acceleration have included various means of applying pressure to the head and/or neck in an attempt to resist the blood shift and to decrease the baroreceptor response. Neck-sealed pressurized helmets, experimented with by the U.S. Air Force in the 1950's, were pressurized with positive pressures of 100 mmHg with good results, but required the aircrew member to hold his breath to protect from overinflating the lungs and to hold his mouth open to equalize pressure between the ears and sinuses. Arterial occlusion cuffs on lower extremities, to diminish venous return from the legs, have been used with some success to at least reduce cephalad venous pressure. Unfortunately, these methods have not provided a fully successful solution to the problems of -G.sub.z acceleration.
Applying a negative pressure (relative to the pressure of the atmosphere surrounding the body) to the lower body of a human, called lower body negative pressure or LBNP, has been used to resist the shift of blood in addressing problems other than the effects of -G.sub.z acceleration. So-called space adaptation sickness, for example, which results from exposure to weightlessness, is somewhat physiologically similar to the effects of -G.sub.z acceleration. An LBNP suit has been used in Soviet space flights to resist the shift of blood to the head during exposure to zero gravity. NASA has also developed a LBNP suit for possible use by U.S. astronauts during exposure to zero gravity. The NASA suit, described in U.S. Pat. No. 4,421,109 to Thornton, uses a gradiently applied negative pressure (more negative toward the feet) to better simulate the effect of normal gravity on an astronaut. The NASA patent appears to teach that, to be safe, the level of negative pressure surrounding the trunk area of a human should not be too far from atmospheric pressure. Also, both the NASA and Soviet suits visually appear to not cover the abdominal area.
LBNP has also been used as an attempted treatment for congestive heart failure. Negative pressures of -30 mmHg to -50 mmHg were used and did not produced sufficiently successful results to bring about its adoption as a standard treatment.
Despite the prior art teachings of the use of LBNP to alleviate the adverse effects of weightlessness, as a treatment for a variety of medical problems and even to simulate the effects of +G.sub.z accelerations, the prior art has not realized the possible use of LBNP for protecting against the effects of -G.sub.z acceleration. Thus it is seen that there is a need for a lower body negative pressure anti-G suit specifically made for protecting against the adverse effects of -G.sub.z acceleration.
It is, therefore, a principal object of the present invention to provide an LBNP anti-G suit specifically adapted to provide protection against the adverse effects of -G.sub.z acceleration.
It is another object of the present invention to provide an improved LBNP suit for alleviating the adverse effects of exposure to zero gravity environments.
It is yet another object of the present invention to provide an improved LBNP suit that will also work as part of a conventional positive pressure anti-G suit for protecting against +G.sub.z acceleration.
It is a further object of the present invention to provide a use for an LBNP suit that alleviates a variety of harmful medical conditions.
It is a feature of the present invention that, despite its bulky appearance, it is very flexible and does not overly hinder an aircrew member.
It is an advantage of the present invention that it provides aircrew members significant protection against the subjective discomfort from -G.sub.z acceleration, which will greatly increase the operating envelope and operational advantage for fighter aircrew members.
It is another advantage of the present invention that it provides a dual-use anti-G suit that provides protection against both positive and negative G.sub.z accelerations.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.